The present invention relates to hydraulic pumps, although other uses will be apparent from the teachings disclosed herein. In particular, the present invention relates to tandem pumps and Bantam-Duty Pumps (BDPs).
Generally BDP units provide an infinitely variable flow rate between zero and maximum in both forward and reverse modes of operation. Pumps discussed herein are of the axial piston design which utilize spherical-nosed pistons, although variations within the spirit of this invention will be apparent to those with skill in the art and the invention should not be read as being limited to such pumps. One such prior art pump is shown in FIG. 1. The pump is a variable displacement pump 10 designed for vehicle applications. A compression spring 12 located inside each piston 14 holds the nose 16 of the piston 14 against a thrust-bearing 18. A plurality of such pistons positioned about the center of the cylinder block 20 forms a cylinder block kit 22. The variable displacement pump 10 features a cradle mounted swashplate 24 with direct-proportional displacement control. Tilt of swashplate 24 causes oil to flow from pump 10; reversing the direction of tilt of the swashplate 24 reverses the flow of oil from the pump 10. The pump is fluidly connected with a motor to form a pump-motor circuit having a high-pressure side and a low-pressure side through which the oil flows. Controlling the oil flow direction, i.e. changing the high- and low-pressure sides, controls the motor output rotation. Tilt of the swashplate 24 is controlled through operation of a trunnion arm 26. The trunnion arm is connected to a slide, which is connected with the swashplate 24. Generally, movement of the trunnion arm 26 produces a proportional swashplate 24 movement and change in pump flow and/or direction. This direct-proportional displacement control (DPC) provides a simple method of control. For example, when the operator operates a control shaft, e.g., a foot pedal, that control shaft is mechanically linked to the swashplate 24 resulting in direct control. This direct control is to be contrasted with powered control discussed later.
A fixed displacement gerotor charge pump 28 is generally provided in BDP units. Oil from an external reservoir and filter is pumped into the low-pressure side by the charge pump 28. Fluid not required to replenish the closed loop flows either into the pump housing 30 through a cooling orifice or back to the charge pump 28 inlet through a charge pressure relief valve. Charge check valves 32 are included in the pump 10 and end cap 34 (cap 34) to control the makeup of oil flow of the system. A screw type bypass valve 36 is utilized in the pump 10 to permit movement of the machine (tractor, vehicle, etc.) and allow the machine to be pushed or towed. Opening a passage way between fluid ports with the bypass valve 36 allows oil to flow, thereby opening the pump-motor circuit, which allows the motor to turn with little resistance because the vehicle wheels will not back drive the pump 10.
FIG. 2 shows an exploded isometric view of a symmetric hydraulic pump 40 (also more generally referred to as pump 40) is connected to a motor in a vehicle via hoses. Typically the hoses are high-pressure hoses. Each symmetric pump 40 includes a symmetric housing 42 and a symmetric end cap 44. The housing 42 is rotated relative to the end cap 44 to position a control arm as desired. The term xe2x80x9csymmetricxe2x80x9d does not imply identical structural symmetry, but rather implies functional or application symmetry. The end cap 44 should be sufficiently functionally symmetric to connect to the housing 42 in one of at least two positions, wherein the other position is rotated relative to the first position. For many applications, the housing 42 and the end cap 44 are rotated 180 degrees relative to one another about a predetermined axis, such as the axis of a pump shaft. In a like manner, a symmetric housing 42 is sufficiently symmetric to achieve an objective whether fitting with an end cap, a vehicle, or the like.
A bypass valve 46, also referred to as a bypass spool, is positioned generally opposite one of the system ports to provide easier access to the bypass valve 46 and a cleaner, more direct, closed loop connection.
The symmetric housing 42 rotatably supports a pump shaft 48. The symmetric end cap 44 includes a porting system discussed more fully, along with pumps generally, in U.S. Pat. No. 6,332,393 (commonly assigned herewith) and incorporated herein by reference. In a symmetric end cap 44 the porting system is preferably bi-laterally symmetric, with regards to the system ports. The porting system includes a pair 51 of system ports (52 and 54) opening external to the end cap 44. The porting system preferably includes a pair of check orifice assemblies that open external to the end cap 44 and connect with the system ports 51.
The porting system generally includes at least one case drain orifice 56 (and may include a pair of orifices) opening external to the end cap 44. The case drain 56 is a drain or connection that diverts excessive fluid (e.g. leakage fluid from the pistons) to a reservoir, thereby reducing pressure in the pump housing 42.
Advantages of the above prior art were not heretofore available because neither a direct displacement tandem pump nor a bantam-duty tandem pump existed heretofore. Tandem pumps are typically of the, relatively, heavy-duty variety and specifically designed to interface with one another. All prior art tandem pumps include an indirect proportional powered control such as a hydraulic and electro-mechanical devices (and combinations thereof) to provide powered control to move the swashplate. So, heretofore, a direct displacement tandem pump did not exist. A particular embodiment of the present invention combines the advantages of a direct displacement bantam-duty pump and a tandem pump; other advantages will be apparent to those with skill in the art from the teachings herein.
The present invention improves on the prior art by providing a tandem pump comprising pumps connected by an interface, rather than pumps specifically designed for a tandem connection. In a particular embodiment the tandem pump comprises a first pump having a shaft end, a cap end and an oil port; and a second pump axially aligned with the first pump and having a shaft end, a cap end, and an oil port. An interface plate connects the shaft end of the second pump to the cap end of the first pump. A conduit connects the oil port of the second pump with the oil port of the first port.
One embodiment is directed toward a tandem pump comprising direct displacement bantam-duty pumps connected by an interface. Those of skill in the art will understand that the present invention more generally provides a means for creating a tandem pump from pumps not specifically designed for such application.
One embodiment of the invention is directed toward a pump interface for connecting an end cap of a first pump to a housing of a second pump. The interface comprises a first side adapted to mate with the end cap of the first pump; and a second side adapted to mate with the housing of the second pump. A pump lumen (i.e., a passage through the pump), preferably through the center of the interface, allows a pump shaft positioned in the first pump to be coupled to a pump shaft positioned in the second pump.
The present invention may be used to allow standard off-the-shelf pumps, not tandem designed, be placed in tandem. Accordingly, one embodiment of the invention is directed toward an interface kit for connecting two pumps in axial alignment to form a tandem pump.
An object of the invention is to provide two pumps with a single input, i.e., a tandem pump, using non-design specific pumps.
Another advantage is to compensate for tandem pump loads and allow use of lightweight pumps, where tandem pump loads are heavier at the second pump than at a single pump.
Another object is to reduce input connectivity for a tandem pump. A specific object is directed toward eliminating the need for a T-box connection to the individual, linked, pumps. A further specific object is to eliminate the need for a complex belt-pulley input system, e.g., a double pulley system or an elongated belt following a cross-vehicle path may be eliminated while obtaining the advantages of a tandem pump.
Another advantage is that the present invention fits in a smaller space due to simpler pump connectivity. A further object is to provide customized tandem pump orientations with ease.